vector iterator incompatible c++ - c++

Question

I've searched all over stackoverflow but just can't seem to find what i'm looking for, so here goes..
I have 2 custom classes one being used in the second and when i'm trying to sort the second class.. which is essentially a vector of the first class it throws the error : - message 0x010c3e18 "vector iterators incompatible" const wchar_t *at vc\include\vector line 238 .. here is my code :
#include <iostream>
#include <conio.h>
#include <cmath>
#include <string>
#include <vector>
#include <fstream>
#include <algorithm>
using namespace std;
class cityPhone {
private:
string cityName;
string cityCode;
public:
void setCode(string code){
cityCode=code;
}
void setName(string name){
cityName=name;
}
cityPhone(){
cityName="Varna";
cityCode="0888123123";
}
cityPhone(string name, string code){
cityName=name;
cityCode=code;
}
string getCity(){
return cityName;
}
string getCode(){
return cityCode;
}
};
//struct { //ive used these 2 also and still it doesnt work
// bool operator()(cityPhone a, cityPhone b)
// {
// if (a.getCity().compare(b.getCity())>0)return true;
// return false;
// }
// } cmpCity;
// struct {
// bool operator()(cityPhone a, cityPhone b)
// {
// if (a.getCode().compare(b.getCode())>0)return true;
// return false;
// }
// } cmpCode;
bool cmpCity(cityPhone a, cityPhone b) // i'm using these 2 in the sorting method
{
if (a.getCity().compare(b.getCity())>0)return true;
return false;
}
bool cmpCode(cityPhone a, cityPhone b)
{
if (a.getCode().compare(b.getCode())>0)return true;
return false;
}
class phoneDirectory {
private :
vector<cityPhone> data;
public:
phoneDirectory (string path){
read(path);
}
phoneDirectory (){
data=vector<cityPhone>();
}
void read(string path){
cout<<endl;
try {
string line;
ifstream myfile (path);
cityPhone bla = cityPhone();
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
try{
bla = cityPhone(line.substr(0,line.find_first_of(" ")),line.substr(line.find_first_of(" ")+1));
data.push_back(bla);
}
catch(exception){ }
}
myfile.close();
}
else cout << "Unable to open file";
} catch (exception) {}
}
void addCityPhone(string city,string phone){
try{
data.push_back(cityPhone(city,phone));
}
catch(exception){
cout<<"Error adding item "<<endl;
}
}
void delCityPhone(int index){
try{
vector<cityPhone>::iterator p=data.begin();
p+=index;
data.erase(p);
}
catch(exception){
cout<<"Error deleting item with index "+index<<endl;
}
}
cityPhone getCityPhone(unsigned index){
try{
vector<cityPhone>::iterator p=data.begin();
p+=index;
return *p;
}
catch(exception){
cout<<"Error deleting item with index "+index<<endl;
return cityPhone();
}
}
vector<cityPhone> getData(){
return data;
}
void phoneChange(string city, string newPhone){
try{
int i=0;
vector<cityPhone>::iterator p=data.begin();
for(p=data.begin();p<data.end();p++,i++){
if (getCityPhone(i).getCity().compare(city)==0){
string oldPhone = getCityPhone(i).getCode();
getCityPhone(i).setCode(newPhone);
cout<<"Phone of city "+city + " was changed from "+oldPhone + " to " + newPhone<<endl;
return;
}
cout<<"No such city exists!\n";
}
}
catch(exception){
cout<<"Error changing phone"<<endl;
}
}
friend istream& operator>>(ostream& out,phoneDirectory a);
friend ostream& operator<<(ostream& out,phoneDirectory a);
};
istream& operator>>(istream& in,phoneDirectory& a){
string city,phone;
in >> city >> phone;
a.addCityPhone(city,phone);
return in;
}
ostream& operator<<(ostream &out, cityPhone a){
return out << a.getCity() <<" " << a.getCode() <<endl;
}
void sortByCity(phoneDirectory a){//with these two i try to sort
vector<cityPhone>::iterator p=a.getData().begin();
vector<cityPhone>::iterator q=a.getData().end();
std::sort(p,a.getData().end(),cmpCity);
}
void sortByCode(phoneDirectory a){
vector<cityPhone>::iterator p=a.getData().begin();
vector<cityPhone>::iterator q=a.getData().end();
std::sort(p,q,cmpCode);//i've tried with std::sort(a.getData().begin(),a.getData().end(),cmpCode) still no effect
}
//bool wayToSortCity (cityPhone a, cityPhone b){ //i've tryed also with these , still no effect
//if (a.getCity().compare(b.getCity())>0)return true;
//return false;
//}
// bool wayToSortCode (cityPhone a, cityPhone b){
//if (a.getCode().compare(b.getCode())>0)return true;
//return false;
//}
int main()
{
phoneDirectory test("C:\\t.txt");
sortByCity(test);//here it crashes
for(unsigned i=0;i<test.getData().size();i++)
cout<<test.getCityPhone(i);
cin>>test;
//test.sortBy(1);
system("pause");
return 0;
}

Answer 1

The problem is that phoneDirectory::getData returns a copy of the data member, so each iterator "belongs to" a different vector.
You need it to return the actual member, not a copy of it.
const vector<cityPhone>& getData() const
{
return data;
}

Answer 2

You have
void sortByCity(phoneDirectory a){//with these two i try to sort
vector<cityPhone>::iterator p=a.getData().begin();
vector<cityPhone>::iterator q=a.getData().end();
std::sort(p,a.getData().end(),cmpCity);
}
Problems with that function:
a.getData() returns a copy of the private data by value. Hence, p and q are iterators on different vectors. Comparing them leads to undefined behavior. You are not comparing p with q but you are comparing p with getData().end(), which is essentially the same thing.
Since the return value is a copy of the member data of a, these are temporary objects. The objects get destructed after the execution of the lines. p and q are the equivalent of dangling pointers.
The argument to the function is an object. After the above errors are fixed, you'll end of sorting a copy of the argument used to call the function. In the calling function, you still won't notice any difference.
The function sortByCode suffers from the same errors.
How to fix the problems
Change the argument type of the function to a reference.
void sortByCity(phoneDirectory& a){
With that change, you will notice any changes to the object in the calling function.
Change the return value of phoneDirectory::getData() to a reference.
vector<cityPhone>& getData(){
return data;
}
That will not only fix all the errors but it will also sort the contents a and not a copy of the contents of a.